Oxidative dehydrogenation of hydrocarbons

ABSTRACT

Hydrocarbons such as butene may be oxidatively dehydrogenated to eg butadiene by use of a catalyst consisting essentially of oxides of molybdenum, cobalt, and boron.

Umted States Patent 1191 1111 3,887,631 Yaffe June 3, 1975 [54] ()XIDATIVE DEHYDROGENATION ()F 3,414,631 12/1968 Grasselli et al 260/680 E H A 3,577,477 5/1971 Boutry et al. 260/680 E YDROC RBONS 3,607,966 9/1971 Croce et al 260/680 E Inventor: Roberta Yaffe, Flshklll, N 3,759,840 9/1973 Barker 252/432 3,764,632 10/1973 Takenaka et al...... 260/680 E [73] Assgnee Texac" New 3,778,386 12/1973 Takenaka et a]. 252/432 [22] Filed: May 14, 1973 [21] APPL 359,953 Primary Examiner-Paul M. Coughlan, Jr.

Attorney, Agent, or FirmT. H. Whaley; C. G. Ries; Carl G. Seutter [52] US. Cl 260/680 E; 252/432; 260/683.3 [51] Int. Cl. C07c 5/18 [58] Field 61 Search 260/680 E ABSTRACT Hydrocarbons such as butene may be oxidatively de- [56] References C'ted hydrogenated to eg butadiene by use of a catalyst con- UNITED STATES PATENTS sisting essentially of oxides of molybdenum, cobalt, 3,159,688 12/1964 Jennings et al 260/680 E and boron- 3,320,330 5/1967 Callahan et al. 260/680 E 3,3 80,931 4/1968 Ryland 260/680 E 6 Clam, Drawmgs OXIDATIVE DEHYDROGENATION OF I-IYDROCARBONS FIELD OF THE INVENTION This invention relates to the oxidative dehydrogenation of hydrocarbons. More particularly it relates to a catalyst system particularly characterized by its ability to promote oxidative dehydrogenation.

BACKGROUND OF THE INVENTION As is well known to those skilled in the art, it is possible to prepare unsaturated hydrocarbons by various processes. For example, 1,3-butadiene may be prepared by dehydrogenation of n-butylenes or by the cracking of eg naphtha which yields a product stream from which 1,3-butadiene may be recovered.

These processes have been continuously reviewed in order to permit attainment of reaction conditions which yield effluent streams characterized by increased yields of desired unsaturated hydrocarbon products.

It is an object of this invention to provide a catalyst and a process for oxidative dehydrogenation of hydrocarbons. Other objects will be apparent to those skilled in the art.

STATEMENT OF THE INVENTION In accordance with certain of its aspects, the novel process of this invention for oxidative dehydrogenation of hydrocarbons may comprise contacting a more saturated charge hydrocarbon in vapor phase in the presence of oxygen with a catalyst consisting essentially of molybdenum oxide, cobalt ox ide, and boric oxide;

maintaining said charge hydrocarbon in contact with said catalyst for 0.5-7 seconds at 350C-550C thereby selectively forming effluent gas containing a less saturated hydrocarbon; and

recovering said effluent gas containing said less saturated hydrocarbons.

DESCRIPTION OF THE INVENTION The more saturated charge hydrocarbon which may be treated by the process of this invention includes hydrocarbons which contain hydrogen atoms which can be removed by oxidative dehydrogenation to yield less saturated product hydrocarbons. The more saturated charge hydrocarbon may include paraffins (which may be treated by the process of this invention to yield mono-olefins) or mono-olefins (which may be treated by the process of this invention to yield di-olefins).

The preferred more saturated charge hydrocarbons may be those containing at least about 4 and preferably 4-8 carbon atoms. It is also preferred that the charge more saturated hydrocarbon be one which is in the vapor state at the conditions of operation.

Typical of the paraffms which may be included in the more saturated charge hydrocarbon feed may be:

n-butanc 2-methylbutane n-pentane cyclohexanc 2-cthylhexane Typical of the mono-olefins which may be included in the more saturated charge hydrocarbon feed may be:

l-butene 2-butene l-pentene 2-pentene 3-pentene Z-methyll -pentene 2-methyl-3-pentene l-hexene l-octene l -phenyl-1 -butene cyclohexene 2-hexene 3-heptene Preferably the more saturated charge hydrocarbon may be a mono-olefin such as a butene, more preferably 2butene.

The oxygen which may be present during the reaction may be as pure oxygen, air, oxygen-enriched air, etc. Most commonly the oxygen may be provided as air.

The catalyst which may be employed in practice of the oxidativedehydrogenation process of this invention may be a composition which can be represented as consisting essentially of molybdenum oxide, cobalt oxide, and boric oxide, the mole ratio of cobalt oxide to molybdenum oxide preferably being about 1:1.

The preferred catalyst may typically be prepared by dissolving 108-180 parts (0.75-1.25 moles), preferably 137-151 parts (0.95-1.05 moles), say 144 parts (1.0 moles) of molybdenum oxide M00 in 97-338 parts (0.75-2.5 moles), say 270 parts (2.0 moles) of 28-30% aqueous ammonium hydroxide. The solution may be diluted with water to form a charge ammonium molybdate solution having a concentration of 0.20.3 molar, say 0.24 molar.

To the ammonium molybdate solution, there may then be added boric acid in amount of 50-125 parts (0.81-2.02 moles), preferably -100 parts 1.21-1.62 moles), say parts (1.46 moles).

A charge cobalt nitrate solution may be prepared by dissolving 218-364 parts (0.75-1.25 moles), preferably 276-305 parts (0.95-1.05 moles), say 291 parts (1.0 mole) of cobalt nitrate hexahydrate Co(NO .6H O in 300-500 parts, preferably 350-450 parts, say 400 parts of water. This solution may be heated to incipient boiling typically C and then added to the charge ammonium molybdate-boric acid solution, the latter also being at incipient boiling temperature, typically 95C.

Upon mixing the charge ammonium molybdate solution and the charge cobalt nitrate solution, a purple precipitate is formed. This precipitate is filtered, dried at 75C-95C, and calcined in a stream of air at 350C-450C, preferably 400C for 3-5 hours, preferably about 4 hours.

The dried precipitated oxide catalyst may, in the preferred embodiment correspond to the formula (I COO-b M0031 8203 wherein a is 0.75-1.25, preferably 0.95-1.05. say 1.0, b is 0.75-1.25, preferably 0.95-1.05, say 1.0, and t is 0.8-2, preferably 1.2-1.6, say 0. 1.5. It will be apparent COO-M003. 1 B203 Commonly, the dried precipitate may be ground to a particle size of 4-16 mesh, preferably about 8 mesh; and in the preferred embodiment, this catalyst may be used in the form of a gravity-packed bed.

Practice of the oxidative dehydrogenation process of this invention may be carried out by passing charge more saturated hydrocarbon, in vapor phase in the presence of oxygen, into contact with the bed of catalyst. 0.25-20 parts, preferably 0.5-5 parts, say 1 part of more saturated charge hydrocarbon and 80-9975 parts, preferably 95-99.5 parts, say 99 parts of oxygencontaining gas may be charged. The oxygen-containing gas may be air, pure oxygen, oxygen-enriched air, etc., containing 21-100%, say 21% by weight of oxygen. The preferred oxygen-containing gas may be air. Steam may be present as diluent.

When the concentration of hydrocarbon falls within the limits of its explosive range, extra caution should be observed.

The space velocity (volume of gas per volume of cat- 'alyst per hour) VHSV may be 500-8000, preferably 1000-4000, say 2010. the corresponding time during which the gas stream is in contact with the catalyst bed may be 0.5-7 seconds, preferably 1.1-2.8 seconds, say about 1.8 seconds.

Commonly the charge may be a stream of air containing about 1% by weight of Z-butene. The charge more-saturated hydrocarbon and the oxygen may be heated to charge temperature of 350C-5 50C, preferably to at least about 400C, say 440C-510C, typically to about 502C; and the reaction is carried out at this temperature. It will be found in practice of this invention that the conversion, selectivity, and yield may decrease substantially as the reaction temperature decreases below 400C unless the volume hourly space velocity VHSV is decreased substantially below about 4000; and accordingly a temperature of about 400C may represent a practical preferred minimum temperature.

It may be noted that if one plots the percent conversion as a function of the value of the product of the temperature of reaction in degrees absolute and the reaction time in seconds, the attainment of conversion over 50% calls for a product value greater than about 940. This may be achieved, for example, by use of a time of 1.8 seconds and a temperature of eg 480C which gives a product of 1355. Preferably, this product may be in the range of 1350-3000, and more preferably about 1350-2000. This empirical relationship may permit one to fix practical operating conditions.

During the reaction, as thegaseous mixture passes through the catalyst bed, the charge more saturated hydrocarbon is subjected to oxidative dehydration and converted to less saturated hydrocarbon. When the charge more saturated hydrocarbon is butane, the product less saturated hydrocarbon produced may be a butene. When the charge more saturated hydrocarbon is a butene, say Z-butene, in the preferred embodiment, the oxidative dehydrogenation may be found to produce 1,3-butadiene in recoverable proportions.

The content of undesirable oxygenated products (such as e.g. butyl alcohol, maleic anhydride, butyric acid, etc.,) is less than 1%; and commonly these undesired byproducts may not be found in the product in determinable quantity.

Typical effluent from oxidative dehydrogenation, e.g. of 2-butene, shows a conversion of up to -90%, and a selectivity of 2040%. Commonly, the off-gas contains as the only hydrocarbons the desired e.g. 1,3- butadiene together with unconverted 2-butene (plus small quantities of l-butene resulting from the isomerization of Z-butene); and the desired product may be readily recovered from the effluent.

PRACTICE OF PREFERRED EMBODIMENTS Practice of the process of this invention may be apparent to those skilled in the art from the following examples wherein, as elsewhere in this specification, all parts are parts by weight unless otherwise stated.

EXAMPLE I In this example which represents practice of the process of this invention, catalyst may be prepared (following the teaching of US. Pat. No. 2,691,660 q.v. also US. Pat. No. 2,625,519) by dissolving 144 parts (1 mole) of molybdenum oxide M00 in 270 parts (2 moles) of concentrated aqueous ammonium hydroxide, and then diluting the resultant solution with water to yield 4000 parts of c. 0.25 molar aqueous ammonium molybdate solution. 100 parts (1.62 moles) of boric acid H 30 may then be dissolved in the solution which may then be heated to C.

291 parts (lmole) of cobalt nitrate hexahydrate Co(- NO .6 H O may be dissolved in 400 parts of water and heated to 95C. This heated solution may be poured into the molybdate-borate solution to yield a purple precipitate which is recovered by filtration, dried, and calcined in air at 400C for 4 hours. The dried catalyst may be ground to 4-12 mesh size and placed within a 1.25-inch diameter tubular Vycor fixed bed reactor containing about cc of catalyst.

A charge stream of air containing 1% of 2-butene may be heated to 416C (780F) and passed through the catalyst bed at space velocity VHSV of 4020 volumes/volume/hr. This corresponds to a time of reaction of about 1.25 seconds. The exit stream is passed through a water scrubber and then analyzed. The hydrocarbon portion of this stream contains 85% of 2- butene, 2% of l-butene, 5% of 1,3-butadiene, less than 1% of other hydrocarbon constituents, and less than 1% of oxygenated hydrocarbons (e.g. maleic anhydride, butyric acid, etc.). The conversion in this example may thus be 15%; the selectivity may be 33.3%.

EXAMPLES ll-lV In these examples which illustrate practice of the process of this invention, the procedure of Example I is followed except that the temperature and space velocity are varied. The conditions of operation and the results are set forth in tabular form in the Table which follows the examples.

EXAMPLE V In this example which represents practice of the process of this invention, catalyst is prepared (following the teaching of Bissot and Benson Ind. Eng. Chem. Prod. Res. Dev. 2 57-60 (1963) by dissolving 144 parts (1 mole) of molybdenum oxide M in 130 parts of 28% aqueous ammonium hydroxide and diluting the resulting solution with 2400 parts of water to yield ammonium molybdate solution. 75 parts (1.22 moles) of 6 while control Example VII at 391C and VHSV of 4020 gives no evidence of reaction. The product of the temperature (664A) and the time (1.25 seconds) in Example VII is only 832; and attainment of desired reacboric acid H 80 are dissolved in the solution which is tion requires that this product value be raised at least then heated to 95C. to about 940. For example, if the temperature be raised A solution of 291 parts (1 mole) of cobaltous nitrate to eg 415C, the product value is 860 and the converhexahydrate Co(NO .6 H in 600 parts of water at sion would be 15%. Increasing the temperature to 95C is poured rapidly into the molybdate-borate solu- 482C, raises the product value to about 947 and the tion yielding a purple precipitate which is filtered, 10 conversion is about 49%. dried, and calcined in air at 400C for 4 hours. The cal- Although this invention has been illustrated by refercined catalyst is ground to finely divided for ence to specific embodiments, it will be apparent to mesh Size) and Placed Within a i-25-inch diameter those slilled in the art that various changes and modifibular Vycor eactor which olds a fi ed pying cations may be made which clearly fall within the scope c. 100 cc. of this invention.

A charge stream of air containing 1% of 2-butene is I cl im; heated to 482C and Passed gh the cata- 1. The method of preparing butadiene from butene lyst at a space velocity VHSV of 2010 for 2 hours. The hi h comprises hydrocarbon portion of the exit gas stream upon analycontacting id but ne i v por phase in the presence sis is found to conta 5 2- 3% l-blltcnc, of oxygen with a catalyst consisting essentially of 24% 1,3-butadie'ne, less than 1% of other hydrocarbon constituents, and less than 1% oxygenated hydrocara b M003 c B203 bons. wherein a is 0.75-1.25, b is 0.75l.25, and c is 0.8-2; maintaining said butene in contact with said catalyst EXAMPLES II-VII 25 for 0.5-7 seconds at 440C-5l0C thereby forming Example VI represents practice of the process of this effluent gas containing butadiene; and invention using the catalyst of Example V. Control Exrecovering said effluent gas containing said butadiample VlI, using the same catalyst, is carried out at ene. 391C, a temperature below the preferred minimum of 2. The method of preparing butadiene as claimed in 400C. claim 1 wherein said catalyst is C00. M00 0.8-2

In the Table which follows, all runs were carried out B 0 over two-hours duration except for Examples 11 and VI 3. The method of preparing butadiene from butene which were carried out for one hour. The space velocas claimed in claim 1 wherein said charge butene is adity Vl-ISV was 4020 in Examples I, II, VI, and VII, 2010 mitted to the catalyst at a volume hourly space velocity in Examples 111 and V, and 1005 in Example IV. All val- VHSV of 500-8000. ues in the Table are in mole percent except for the 4. The method of preparing butadiene from butene contact time which is in seconds, and the temperature as claimed in claim 1 wherein said charge butene is adwhich is in degrees Centigrade. mitted to the catalyst at a VHSV of 1000-4000.

TABLE Example Temp. "C Time 2-Butene l-Bptene 1,3-Butadiene Conv. Selec.

| 415 1.25 2 5 15 33.3 11 482 1.25 51 5 19 49 38.7 111 502 2.5 25 5 24 75 32.0 IV 502 5 16 5 20 84 23.8 V 482 1.25 35 3 24 65 37.0 v1 482 1.25 58 4 13 42 31.0 Vll* 391 2.5 0 0 0 0 *Control From the above table, it will be apparent that satisfactory results may be achieved in the conversion of 2- butene to 1,3-butadiene by practice of the process of this invention. Typically a conversion of up to about 84% of the charge 2-butene may be achieved with a selectivity as high as 38 It will be apparent that the reaction may be controlled to give high conversion or high selectivity; and

high conversion may frequently be achieved at the expense of high selectivity.

It will also be apparent from comparison of Examples VI and VII that experimental Example VI at 482C and VHSV of 4020 gives 42% conversion at 31% selectivity 5. The method of preparing butadiene from butene 5 as claimed in claim 1 wherein said charge butene is ene. 

1. The method of preparing butadiene from butene which comprises contacting said butene in vapor phase in the presence of oxygen with a catalyst consisting essentially of a CoO. b MoO3 . c B2O3 wherein a is 0.75-1.25, b is 0.75-1.25, and c is 0.8-2; maintaining said butene in contact with said catalyst for 0.5-7 seconds at 440*C-510*C thereby forming effluent gas containing butadiene; and recovering said effluent gas containing said butadiene.
 1. THE METHOD OF PREPARING BUTADIENE FROM BUTENE WHICH COMPRISES CONTACTING SAID BUTENE IN VAPOR PHASE IN THE PRESENCE OF OXYGEN WITH CATALYST CONSISTING ESSENTIALLY OF
 2. The method of preparing butadiene as claimed in claim 1 wherein said catalyst is CoO. MoO3 . 0.8-2 B2O3.
 3. The method of preparing butadiene from butene as claimed in claim 1 wherein said charge butene is admitted to the catalyst at a volume hourly space velocity VHSV of 500-8000.
 4. The method of preparing butadiene from butene as claimed in claim 1 wherein said charge butene is admitted to the catalyst at a VHSV of 1000-4000.
 5. The method of preparing butadiene from butene as claimed in claim 1 wherein said charge butene is contacted with said catalyst for 1.1-2.8 seconds. 